Unloading of bulk liquid or pulverulent cargoes from cargo ships



Dec. 13, 1966 c. H. CARSLAW 3,291,351 UNLOADING 0F BULK LIQUID OR PULVERULENT 1 CARGOES FROM CARGO SHIPS 1 Filed Nov. 2'7, 1964 2 Sheets-Sheet l 3 i q We n 0 f' if: h I" a j /4 5 VVVW WWV I IF II I! K Z. H IIL' '3; 611 u u u U 7 e U U PF 56.5.

Dec. 13, 1966 c. H. CARSLAW 3,291,351

UNLOADING OF BULK LIQUID 0R PULVERULENT CARGOES FROM CARGO SHIPS Filed Nov. 27, 1964 2 Sheets-Sheet 2 United States Patent Ofifice 3,2913% Patented Dec. 13, 1966 3,291,351 UNLOADING 01F BULK LIQUID R PULVERU- LENT CARGOTES FROM CARGO HIPS Charles Henderson Carslaw, Yoker, Glasgow, Scotland, assignor to Drysdale & Company Limited, Glasgow, Scotland, a corporation of Great Britain and Northern Ireland Filed Nov. 27, 1964, Ser. No. 414,235 Claims priority, application Great Britain, Nov. 27, 1963, 46,812/64 Claims. (Cl. 222464) This invention relates to the unloading of bulk liquid or pulverulent cargoes from cargo ships. The invention is particularly, although not exclusively, applicable to the unloading of crude petroleum oil from the cargo tanks of oil tank ships.

Present trends in shipbuilding are towards large oil tank ships, which may be of the order of 100,000 tons dead weight or more. In the construction of such vessels the required strength of the hull is primarily obtained by the incorporation of a first plurality of closely-spaced, parallel structural members disposed fore and aft and of a further plurality of structural members disposed athwartships, the bottom plates of the hull being rigidly attached, generally by welding, to the undersurface of said members. Some of the first and further pluralities of structural members constitute bulkheads which define cargo tanks in the bottom of each of which a cell structure is formed by the remainder of the first and further pluralities of structural members. In order to pemit the extraction of oil from the cell structure during discharge of the oil from the tank a plurality of strum boxes, which are connected to the suction inlet of the oil discharge pump, have hitherto been mounted in the bottom of the tank, each strum box being located within one of the cells constituted by the structural members. Since, however, it is impracticable to locate a strum box in each cell the practice has been to form apertures, which are known as limber holes, in the structural members adjacent to the bottom of the tank so that oil may flow through said holes to the strum boxes during the discharge of the oil. The viscosity of the oil together with the restriction on the flow thereof through the limber holes, which cannot be increased in cross-sectional area beyond pre-deterrnined dimensions without the risk of seriously weakening of the hull, results in the rate of discharge of the oil, when the mean oil level is below a certain value, being reduced thereby increasing the total time required to discharge the oil. Since it is economically desirable that the time required to unload and, if appropriate, re-load the ship be maintained at a minimum this increase in the time required for the discharge of the oil can be extremely expensive for the ships operators.

It is an object in making the present invention to provide a cargo ship, the bottom of each cargo tank of which is formed with a cell structure as described above, in which the time required to discharge the oil may be appreciably less than the corresponding time under present practice.

In a cargo ship according to the invention the or each cargo tank, adjacent to the bottom thereof, is in the form of a plurality of cells defined by structural members disposed in the fore+and-aft direction and further structural members disposed athwartships, the bottom of the tank being rigidly secured to the further structural members, and at least one trunk extends substantially from side to side of the tank athwartships or in the fore-and-aft direction, the trunk being in communication with the interior of the tank along the longitudinal edge thereof which is adjacent to the bottom of the tank, the trunk being in communication with the suction inlet of a discharge pump, and

limber holes being formed, respectively, in the further structural members, with the exception of bulk heads which bound the tank, or in the structural members, with the exception of the sides of the tank.

The trunk is preferably of substantially L-shape in cross-section, the free edge of one of the limbs of the trunk being secured to one of said structural members or to one of said further structural members and the free edge of the other of the limbs of the trunk, which other limb is downwardly directed, being located a spaced distance, which may be of the order of 1 inch in magnitude, from the bottom of the tank.

According to an alternative embodiment, however, the trunk comprises a main duct to which is connected a plurality of fishtail-shaped suction ducts, the ends of the suction ducts, remote from the main duct, being located in one of the cells in each row of cells disposed parallel to the structural members in which the limber holes are not formed, said ends of the suction ducts being disposed a spaced distance, which may again be of the order of 1 inch in magnitude, from the bottom of the tank. Preferably the fishtail-shap'ed suction ducts are downwardly directed and are inclined at an acute angle to the vertical, the part of the lower end of each suction duct disposed nearest to the vertical through the upper end of the suction duct being cut away to reduce vortex formation.

In order that the invention may be more easily understood and more readily carried into effect the same will now be described more fully with reference to the accompanying drawings in which:

FIG. 1 is an isometric view of a cargo tank of a cargo ship according to a first embodiment of the invention, parts of the tank being broken away for clarity,

FIG. 2 is a sectioned view, to :a larger scale than FIG. 1, of part of the cargo tank shown in FIG. 1,

FIG. 3 is an isometric view of part of a cargo tank of a cargo ship according to a second embodiment of the invention, the parts of the tank which have been omitted being as shown in FIG. 1, and

FIG. 4 is a sectioned view, to a larger scale than FIG. 3, of part of the cargo tank shown in FIG. 3.

With reference to all the figures of the drawings, 1 denotes generally a cargo tank of an oil tank ship, the tank 1 being bounded by a forward bulkhead 2, an after bulkhead 3, the portions of the sides 4 of the ship between the bulkheads 2, 3, and the portion of the bottom 5 of the ship between the bulkheads 2, 3.

A plurality of closely spaced parallel structural mem bers 6, which includes the sides 4 of the ship, is disposed fore-and-aft and a plurality of further structural members 7 which includes the bulkheads 2, 3 and which with the exception of the bulkheads 2, 3 is constituted by partial bulkheads is disposed athwartships. Bottom plates 5 are rigidly attached by welding to the undersurfaces of the members 6, except the sides 4 and 7.

Limber holes 8 are formed in'the members 7 which are disposed athwartships with the exception of the bulkheads 2, 3. Referring to FIGS. 1 and 2, a trunk 9 of L-shape in cross-section is disposed within the tank 1 and extends adjacent to the after bulkhead 3, between the sides 4- of the ship. The free edge of one limb 10 of the trunk 9 is secured to the after bulkhead 3, the limb 10 being disposed substantially horizontally. The free edge of the other limb 11 of the trunk 9 is disposed a spaced distance of approximately 1 inch from the bottom plates 5 of the ship, the limb 11 being downwardly directed.

The trunk 9 is in communication by way of ducts 12 with the suction inlet of a discharge pump (not shown).

Referring to FIGS. 3 and 4, a trunk 13 is disposed within the tank 1 and extends, adjacent to the after bulkhead 3, between the sides 4 of the ship. The trunk 13 comprises a plurality of fishtail-shaped suction ducts 14 which are disposed one within each of the cells defined by the members 6, 7 and which are located adjacent to the after bulkhead 3. The suction ducts 14 are interconnected by a main duct 15 which is in communication with the suction inlet of a discharge pump (not shown).

The suction ducts 14 are downwardly directed from the duct 15 at an angle of approximately 45 to the vertical. The lower, open end of each suction duct 14 is disposed a spaced distance of approximately 1 inch from the bottom plates 5 of the ship, the part of this lower end nearest to the vertical through the main duct 15 being cut away as shown at 16 (FIG. 4) to reduce vortex formation.

Alternatively, the trunks 9, 13 may be disposed foreand-aft instead of athwartships in which case the trunks 9, 13 are disposed adjacent to one of the structural members 6 and the limber holes 8 are formed in the members 6 with the exception of the side 4.

Referring to all the embodiments of the invention it is possible, since the flow of oil to the trunk 9 or 13 during discharge of the oil is in one direction, to pump at full rate until the depth of oil in the tank 1 is approximately 9 inches or less, which compares with a corresponding depth under known practice of the order of 5 feet, before the rate of pumping must be reduced to a value dependent on the rate of How of oil to the cells with which the trunk 9 or 13 is in communication. There is thus a considerable saving in time in the discharge of the oil from the tank 1 with a corresponding saving in expense although, if in any circumstances the time required to discharge the oil is not of importance, the present invention is still applicable since discharge pumps of smaller pumping capacity, and consequently of less expensive manufacture, may be used without increasing the time required for discharging the oil.

What is claimed is:

1. A cargo ship having cargo tanks in which there are first structural members disposed in the fore-and-aft direction, further structural members disposed athwartships, tank bottom means attached to the undersurfaces of said structural members, a plurality of cells defined by said structural members, at least one trunk extending substantially from side to side of the tank in either of the directions comprising the athwartships direction and the foreand-aft direction, the trunk being in communication with the interior of the cargo tank along the longitudinal edge thereof which is adjacent to said tank bottom means, a discharge pump having a suction inlet thereto which is in communication with said trunk, and limber holes formed in the structural members which are substantially parallel to said trunk, with the exception of the structural members which bound the tank.

2. A cargo ship as claimed in claim 1 in which the trunk is of substantially L-shape in cross-section and comprises two interconnected limbs, the free longitudinal edge of one of said limbs of the trunk being secured to one of the structural members and the free edge of the other of said limbs of the trunk being downwardly directed and being located a fixed spaced distance from the bottom means of the tank.

3. A cargo ship as claimed in claim 2 in which said spaced distance is of the order of 1 inch in magnitude.

4. A cargoship as claimed in claim 1 in which said trunk comprises a main duct and a plurality of fishtailshaped suction ducts one end of each of which is connected to said main duct, the other end of each of said plurality of suction ducts being located in one of the cells in each row of cells disposed substantially at right angles to the structural members in which the limber holes are formed, said other end of each of said plurality of suction ducts being disposed a spaced distance from the bottom means of the tank, said plurality of suction ducts being downwardly directed and inclined at an acute angle to the vertical, and a cut-away portion being formed in the part of the lower end of each said suction duct disposed nearest to a vertical through the upper end of said suction duct whereby to reduce vortex formation.

5. A cargo ship as claimed in claim 4 in which said spaced distance is of the order of 1 inch in magnitude.

References Cited by the Examiner UNITED STATES PATENTS 2,710,586 6/1955 Shelton 114-74 FOREIGN PATENTS 815,495 5/ 1959 Great Britain.

191,992 10/1964 Sweden.

ROBERT B. REEVES, Primary Examiner.

I-IADD S. LANE, Examiner. 

1. A CARGO SHIP HAVING CARGO TANKS WHICH THERE ARE FIRST STRUCTURAL MEMBERS DISPOSED IN THE FORE-AND-AFT DIRECTION, FURTHER STRUCTURAL MEMBERS DISPOSED ATHWARTSHIPS, TANK BOTTOM MEANS ATTACHED TO THE UNDERSURFACES OF SAID STRUCTURAL MEMBERS, A PLURALITY OF CELLS DEFINED BY SAID STRUCTURAL MEMBERS, AT LEAST ONE TRUNK EXTENDING SUBSTANTIALLY FROM SIDE TO SIDE OF THE TANK IN EITHER OF THE DIRECTIONS COMPRISING THE ARTHWARTSHIPS DIRECTION AND THE FOREAND-AFT DIRECTION, THE TRUNK BEING IN COMMUNICATION WITH THE INTERIOR OF THE CARGO TANK ALONG THE LONGITUDINAL EDGE THEREOF WHICH IS ADJACENT TO SAID BOTTOM MEANS, A DISCHARGE PUMP HAVING A SUCTION INLET THERETO WHICH IS IN COMMUNICATION WITH SAID TRUNK, AND LIMBER HOLES FORMED IN THE STRUCTURAL MEMBERS WHICH ARE SUBSTANTIALLY PARALLEL TO SAID TRUNK, WITH THE EXCEPTION OF THE STRUCTURAL MEMBERS WHICH BOUND THE TANK. 